Numerous applications exist for electrical power sources (e.g., a battery). One of these applications is within the field of emergency communications. Emergency communications are often required under less than ideal conditions, such as during natural and man-made disasters. Interruption of normal power sources (e.g., household power), and the importance of communicating quickly, can create situations in which power sources can be extremely valuable, for example the use of batteries to power radio or cellular communications during emergency situations.
Another application for electrical power sources occurs in modern military operations, which are increasingly reliant on portable electrical power sources for communication, night vision, and navigation systems (for example navigation systems employing the Global Positioning System). In the event that supply lines are cut off, battery power for these systems may be drained quickly, and access to electrical power can mean the difference between life and death of a soldier.
There are several known approaches to storing mechanical energy for electrical power supply. For small appliance operation, these include wind-up springs, flywheels and batteries. Wind-up springs are typical of the radio sets used in WWII, in which the operator winds a spring that slowly releases energy while the radio is used. Flywheels are often seen in commercial hand-operated flashlights, in which the flywheel is brought up to speed prior to operating the flashlight. The battery approach is exemplified in the automobile starter system, where a battery is used to store energy sufficient to crank over the motor. However, batteries are generally heavy in comparison to the output power they can produce, and can provide only a limited amount of power before they must be recharged or replaced. Other known approaches utilize gravitational potential energy, such as the wind-up clock that employs lifted weights; however, such devices do not lend themselves to light weight or portability due to their use of an elevated mass in a particular orientation.